/*
File Name: error1.cpp
	> Author: 
	> Mail: 
	> Created Time: 一  8/29 21:47:35 2016
 ************************************************************************/

#include<iostream>
#include<cstdlib>
using namespace std;
double hmean(double a, double b);

int main()
{
    double x,y,z;
    cout<<"Enter two numbes: ";

    while(cin>>x>>y)
    {
        z=hmean(x,y);
        cout<<"Harmonic mean of "<<x<<" and "<<y
        <<" is "<<z<<endl;
        cout<<"Enter next set of numbers <q to quit> : ";
    }
    cout<<"Bye !\n";
    return 0;
}

double hmean(double a, double b)
{
    if(a==-b)
    {
        cout<<"untenable argues=ments to hmean() \n";
        abort();
    }
    return 2.0*a*b/(a+b);
}

